Firstly, dreams do not foretell the future. You can only dream about things already IN your subconscious, and the future isn't there. That said, you will dream about anything IN your subconscious, but combined in different ways than real life; your subconscious replays things in the order it finds them when it creates dreams, and our memories are NOT stored in straight lines. So your engagement was in your memories. And "some guy" was in your memories. But while when you remember them they are two separate memories, your subconscious played them where it found them. You might be cautious telling people around you about this; many people assume that if you dream about things in a certain combination, you have been THINKING about them in that same way. Not true, but try to tell that to an upset fiance.